This invention relates to a method for preparing a platelet reference control and, more particularly, a control especially useful with automated counters. The inventive procedure provides a product which meets the demand for quality control in the clinical laboratory for stabilized cellular components of blood to assess the reproducibility and accuracy of counters.
Platelets for platelet reference controls are prepared by reaction with an aldehyde, preferably glutaraldehyde. After appropriate washing by centrifugation to remove the glutaraldehyde and aggregates, the "aldehyde-reacted" platelets are suspended in a phosphate buffer. The suspended platelets are not stable and will aggregate under a number of circumstances. In addition, the "aldehyde-reacted" platelets gradually change shape, shrinking in size as they age.
The aldehyde-reacted platelets are intended to be used in particle counters which are affected by particle size. Thus, the reference control should ideally contain platelets which are as similar as possible in size to the platelet particles in normal human blood. It is apparent that aggregation will affect the count and size of the particles in the reference control. It is also apparent that the shrinking that occurs with time and heat also will impair the value of the control--since the platelets are no longer the same size as platelets in human blood.
The objective was to produce aldehyde-reacted platelets that do not aggregate, which have the same size as platelets in human blood, and which maintain their size for at least six months.
Factors found to affect aggregation of aldehyde-reacted platelets are: ionic strength and pH of the buffer or salt solution; and freezing of the solution. Freezing problems can be avoided by adding 0.5-1.5 molar ethylene glycol (alternatively glycerin or methanol) to the suspension. The size of the platelets can be controlled, i.e., stabilized, through the addition of 0.1-0.3 glycine to the suspension.